Field of the Invention
The present disclosure relates to a small cell system and a method for allocating a resource thereof, and more particularly, to a technology of selecting a base station and allocating an orthogonal frequency division multiplexing (OFDM) resource in a small cell system.
Description of the Related Art
In a conventional cellular system, when selecting a base station, an average signal-to-noise ratio (hereinafter, referred to as SNR) is measured through a downlink pilot to select a base station having the largest SNR. After the base station is selected, each base station independently allocates resources of a serving user. Since all small cells can perform independently user selection and resource allocation without sharing information between small cells by using the above described method, it is most simple in terms of implementation complexity. However, since such a method does not consider at all the interference from other small cells, the SNR performance is not ensured such that the performance is degraded significantly as the density of the small cell becomes higher.
On the other hand, a coordinated multi-point (CoMP) method shares all information such as a channel of all user, data, and the like by a plurality of base stations through a direct link backhaul (e.g., X2 link in a 3GPP LTE system) between base stations and accomplishes cooperatively a resource allocation, a user selection, and a data transmission. Typically, such a cooperative method requires the most expensive cost for the backhaul installation and the highest complexity for the implementation, but it can be expected to achieve a high performance compared to the above independent method.
Since the backhaul exists between small cells within a cluster, such a cooperative user selection and resource allocation method is necessary to increase performance. However, the backhaul between the small-cell base stations defined in the 3GPP has various types ranging from an ideal case of a 10 Gbps to a 10 Mbps wireless backhaul. A compatibility for supporting these various backhauls is essentially required in a next generation LTE system. However, the conventional method has strict requirements necessary for the performance of backhaul for each technology, and lacks a compatibility and a flexibility for supporting various backhaul performances.
In addition, since tens or hundreds of users exist in a next-generation small cell network, there is a limit of cooperatively selecting a user and optimizing the resource allocation with respect to those many users. Furthermore, in order to accomplish the user selection and the resource allocation for optimizing a signal-to-noise-plus-interference ratio (SINR), each user terminal have to measure the signal strength between a plurality of small-cell base stations and report this through a feedback. Hence, there is a burden in that such an overhead significantly increases as the number of users increase.